Electric discharge apparatus



23, 1 5- F. H. GULLIKSEN 2,367,940

ELECTRIC DISCHARGE APPARATUS Filed Sept. 7, 1939 INVENTOR WITNESSES:

(2% Fi'nn/ifiu/llksen,

' ATT NEY Patented Jan. 23, 1945 ELECTRIC DISCHARGE APPARATUS Finn H. Guiliksen, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh; Pa., a corporation of iennsylvania Application September 7, 1939, Serial No. 293,731

5 Claims. (pl. 250-27) My invention relates to electric discharge apparatus and has particular relation to ignitrons.

In accordance with the teachings of the prior art of which I am aware, an electric discharge valve such as a thyratron is used to control the firin of an ignitron. The thyratron is interposed in circuit with the ignition electrode and the pool of the ignitron and at the instant of firing conducts ignition current through the ignition current through the ignition electrode. Since the ignition current required is of substantial magnitude, the thyratron must necessarily be relatively large. Because of the care which is essential in the construction of a thyratron, the valve is relatively expensive and substantially increases the cost of the equipment.

It is an object of my invention to provide a simple and inexpensive firing system for an ignitron. Y

Another object of my invention is to provide a firing arrangement of simple structure for an ignitron that shall have all of the advantages of the thyratron.

An ancillary object of my invention is to vide a novel spark gap.

A specific object of my invention is to provide apparatus of simple and inexpensive structure for controlling the supply of alternating current from a source to a load.

Mor concisely stated, it is an object of my invention to simplify the apparatus used for controlling ignitrons.

In accordance with my invention, the ignition current for an ignitron is supplied through a discharge gap. The gap is interposed in the ignition,

circuit and conducts current through the igniter when the firing is to take place. I have found that an air gap is particularly adapted for the practice of my invention, although in its broader aspects it may be carried out with a glow discharge gap comprising a plurality of unexcited electrodes disposed in a medium at a pressure which may vary from several millimeters of mercury to a fraction of an atmosphere.

In accordance with the preferred practice of my invention, the spark gap consists ,of'a plurality of main terminals and an ignition terminal disposed adjacent to the main terminals. A spark of a discharge is ignited between the main terminals when a high potential of the order of one thousand to ten thousand voltsis impressed between the ignition terminal and the mainterminals. The igniter is supplied through the main terminals and the control potential for the 3.13 paratus is impressed on the ignition terminal.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. he invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawing, in which the single figure is a diagrammatic view showing a pre ferred embodiment of my invention.

In the drawing, my invention is specifically shown as applied to a resistance welding system in which alternating current is supplied for Welding purposes. The apparatus comprises a welding transformer I across the secondary 3 of which a pair of welding electrodes 5 are connected. The electrodes are in engagement with a material '1 to be welded, and, when the transformer I is energized, current is conducted through the mate rial. The primary 9 of the transformer l is supplied from an alternating current source H through a pair of ignitron l3 and I5 interposed in anti-parallel between the source and the primary. The source I! may be of the usual commercial 60-cycle type. Each ignitron comprises an anode ll, a cathode [9 of the pool type and an ignition electrode 2|.

The current for firing the ignitrons 13. and i5 is supplied through a discharge gap 23 which is preferably of the open-air spark type. The gap comprises a pair of principal terminalsf25 and 21 and an ignition terminal 29. The principal terminals 25 and 21 are interconnected bya high resistor 3| and are individually connected each to an ignition electrode 2| The ignition terminal 29 is connected to the intermediate tap 33 of the resistor through the secondary 35 of a peaking transformer 37. The potential of the secondary 35 is thus impressed between the ignition terminal 29 and the principal terminals 25 and 2'? and the resistor 3! functions to properly distribute it.

The primary 39 of the peaking transformer Si is supplied through a thyratron ll of relatively small rating or from a high vacuum valve from a capacitor 43. The capacitor 43is maintained charged from th source I I through a suitable rectifier 45 and the polarity of the charge is such that when the thyratron is non-conductive it impresses a positive potential between its anode 41 and its cathode 49. The control electrode 5! of the thyratron 4| is connected to the cathode 49 in control contactor 53, through a rectifier 55 and a biasing potential 51. The rectifier 55 is supplied from the secondary 59 of another peaking transformer 5|. The phase in the half cycles of the source II at which the impulses are supplied by the peaking transformer 6| is determined by a rheostat 63 in series with the primary 65 of the transformer. The biasing potential 57' is of such polarity that when the contact 53 is first closed the valve 4! is maintained non-conductive. The rectifier 55 'is'interposed between the control electrode 5! and the secondary 59 of the transformer 5| in such a sense that an impulse counteracting the biasing potential is supplied during each .half period of the source H. The contact 53 maybe the circuit controller of any suitable timing arrangement for welding.

To initiate welding operation, the timing contact 53 is closed. The contact interconnects the control electrode 5| and the cathode 49 of the valve H, the cathode and the two sources of potential 55 and 51 and, as a result, the valve is rendered conductive at instants predetermined by the setting of the rheostat 63 during each of a number of half periods of the source. The capacitor 43 in the valve circuit is then discharged through the primary 39 of the firstmentioned peaking transformer 31 and a high potential is impressed through the secondary 35 between the ignition terminal 29 and the main terminals 25 and 21 of the discharge gap 23. The main terminals are connected across the source through the igniters 2| andthe cathodes |9 of the main valves '|3 and I5. The combined influence o'f'the source potential and the high potential supplied by the peaking transformer 31 is to ignite a, discharge or, preferably, a spark between the main terminals. For the purpose of explaining the operation, let us assume that at the instant of ignition of the discharge the upper terminal 61 of the source I .is positive and its lower terminal 69'negative. Under such circumstances, current flows in a circuit extending from the upper terminal .51 through the primary *9 of the transformer l, the cathode I9 and the ignition electrode 2| of the right-hand ignitron I5, the spark terminals 25 and 21, the ignition electrode 2] and the cathode I9 of the left-hand ignitron |3, to the lower source terminal 69. The anode-cathode potential of the left-hand ,ignitron I3 is at this time positive, and, at the same time, the current through its ignition electrode 2| is of the proper polarity to render it conductive. The left-hand lgnitron therefore becomes conductive and current flows through the primary "9 vof the welding transformer The ignitron I3 is fired immediately .after the discharge gap '23 is ignited. After the ignitron becomes conductive, the potential between its anode I! and its'cathode l9 and therefore the potential across the discharge gap 25-21 .and the ignition-electrode and cathode of the righthand ignitron 25, becomes equal to the arcdrop potential. Since this potential is relatively small, the current flow through the ignitionelectrode 2| of the right-hand ignitron 25 and .the spark gap 25- 21 is materially reduced.

Atan interval of the order of .the half period of the source later the source polarity reverses and the potential .across .the left-hand ignitron I3 becomes too small to sustain the discharge and the valve is extinguished. Thereafter another impulse is impressed in the control circuit .of the auxiliary valve -4|, and :the capacitor 43 which was charged while the lefthand .ignitron was conductive is again discharged. The spark gap 23 is then again ignited and this time the righthand ignitron 25 is rendered conductive. The ignitrons thus continue to conduct current alternatingly until the timing contact 53 is opened and-the auxiliary valve 4| remains non-conductive.

.In the following claims the .term spark-gap means a pair of terminals separated continually when in use by a gap in air of substantial length. The term ignitron means an electric gaseous discharge tube fin which initiation of current flow from anode to cathode is caused by an auxiliary electrode one end of which contacts said cathode.

Although I have shown and described a certain specific embodiment of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination an ignitron having a plureality of principal electrodes and an ignition electrode, means for impressing a potential between said principal electrodes, circuit means having a spark gap interposed therein for supplying ignition current to said ignition electrode. said spark gap having a pair of spark terminals and an ignition terminal, and means for impressing an ignition potential between said ignition terminal and said spark terminals.

'2. For use in supplying power from an alterhating current source to a load the combination comprising a pair of ignitrons, each having. a plurality of principal electrodes and an ignition electrode, interposed in anti-parallel between said source and said load, a spark gap interposed between said ignition electrodes and means for igniting a spark in saidgap.

3. For use in supplying :power from an alternating current source to a load the combination comprising a pair of ignitrons, each having a plurality of principal electrodes and an ignition electrode, interposed in anti-parallel between said source and said load, a spark gap having a plurality of main terminals and circuit means connecting said terminals between said ignition electrodes.

4. For use in supplying power from an alterhating-current source to a load the combination including electric discharge valve means connected in series circuit with said source and load and including a pair of electrodes .of the pool. type connected through said series circuit to opposite terminals of said souroeand an ignition electrode in contact with each pool electrode. a spark gap, circuit means connecting said gap between said ignition electrodes, and means for igniting a spark in said gap to effect completion of a circuit between said ignition electrodes.

5. For use .in supplying power from an alternating-current source to a load the combination including electric discharge valve means connected in a series circuit with said source and load and including a pair of electrodes of the pool type connected through .said series circuit to opposite terminals of said source and an ignition electrode in contact with each pool electrode, a spark gap connected between said ignition electrodes, said gap including a plurality of main terminals and anignition terminal, and means for impressing a potential between said ignition terminal and said main terminals which is of short duration'compared to a half period of said source for igniting a spark in said gap to effect completion of a circuit between said electrodes.

FINN H. GULLIKSEN. 

